Williamson synthesis of ether is an example of :

The Williamson ether synthesis is the most widely used method to synthesize ethers. It occurs by an ${\mathrm{S}}_{\mathrm{N}}2$ reaction in which a metal alkoxide displaces a halide ion from an alkyl halide.

${\text{RO}}^{-}+{\text{R}}^{\text{'}}-\text{x}\underset{{\text{S}}_{\text{N}}}{\to }\text{R}-\text{O}-{\text{R}}^{\text{'}}$

This is Nucleophilic substitution reaction.